The present invention relates to a construction for attaching a knob to a manipulation rod of a push-button type mechanism.
In the push-button type actuating mechanism such as that for push-button switch, a knob made of synthetic resin is fixedly secured to a outer end of a manipulation rod.
Referring to FIG. 1 showing a construction for connection between the manipulating rod and the knob, reference numeral 1' denotes a known switch body having contacts which are adapted to be switched by vertical movement of a manipulation rod 2'. The manipulation rod 2' is provided at its intermediate portion with a flange 2a' and, at its end, with a fitting recess 2b'. Reference numeral 3' denotes a compression spring acting between the switch body 1' and the flange 2a'.
A knob 4' made of a synthetic resin is provided therein with a fitting projection 4b'. The knob 4' is provided with an attaching portion 4a' on the inside of which is formed a fitting projection 4b'. The knob 4' is attached to the manipulation rod 2' with the attaching portion 4a' receiving the end of the manipulation rod 2' and the fitting projection 4b' engaging the fitting recess 2b'.
The above-mentioned knob 4' is formed in a manner described hereinunder. Referring to FIG. 2A, a mold cavity defined between the upper mold 5' and a lower mold 6' is filled with a synthetic resin injected thereinto. Then, as shown in FIG. 2B, the lower mold 6' is withdrawn as shown in FIG. 2B in the direction of the arrow to separate the upper and lower molds 5', 6' from each other and, as shown in FIG. 2C, the knob 4' attached to the lower mold 6' is pushed by knock-out pins 7' to be thus separated from the lower mold 6'. In separating the knob 4' from the lower mold 6', it is often experienced that the recess 6a' fittingly receiving the fitting projection 4b' undesirably cuts the latter. For this reason, it is difficult to obtain a shape and size of the fitting projection 4b strictly meeting the shape and size of the design. Namely, the variance in the size tends to occur due to a change in molding conditions, the batch of the plastic material and so forth.
It is, therefore, extremely difficult to ensure the strength of the knob 4' against the force which acts to withdraw the knob 4' from the manipulation rod 2', if the knob 4' formed by the above-explained process is snap-fitted onto the manipulation rod 2'. In an extreme case, play occurs between the knob and the rod of the switch due to the above-explained reason. This considerably deteriorates the commercial value of the products. Since the knob 4' generally has a small size, if the above-mentioned force against the withdrawal is increased by increasing the size of the fitting projection solely, the insertion force is undersirably increased possibly resulting in bending of the manipulating rod during the assembly operation.